Genetically created by the Wood Elemental race as a disease for the skin elementals, the Seeder slowly consumes the nutrients of the body and replaces them with wood fiber.
The Seeder appears as simple moss on the wood elemental. When the elemental came into contact with one of the sentient skin elementals, it would brush the moss onto the skin elemental. The moss would immediately adhere to the skin and could not be removed. Over time, that moss would start spreading and the areas that it touch would harden and stiffen. Eventually, one of the victim’s appendages would solidify into a large seed.
After a while, the seed would be too hard to carry and the victim’s body would be too stiff. At this point, the seed would take root and the skin elemental would be replanted as a tree.
The terrifying part of this is that the mind of the skin elemental would still be active during this entire process. This was determined when other telepaths could “hear” Skin Elementals screaming. In some societies, the Skin Elementals were put to death to save them from this anguish and going mad.
Over the years, though, a problem arose. The disease, first engineered to only affect Skin Elementals, began affecting all of the elemental races. It had mutated enough that no race was safe anymore.